The invention relates to a windshield wiper drive device.
For a long time, windshield wiper drive devices have been known in which a rotary motion of a motor that rotates in a predetermined direction is converted into a reciprocating motion of the windshield wiper by means of an eccentric mechanism. Recently, windshield wiper drive devices in which the drive motor is controlled directly in different directions of rotation as a function of the reciprocating motion of the wiper have increasingly been introduced as well. In such drive devices, it is necessary to detect positions of the windshield wiper, at least at the turning points of its motion, so that the direction of rotation of the motor can be reversed at the correct time. Conventional drive devices use separate detectors for the various positions for this purpose, or else a single detector is used to detect a plurality of detectands, in other words objects of arbitrary type that can be detected by a detector; each detectand corresponds to one position to be detected.
This type of position detection for controlling the windshield wiper drive device is complicated and accordingly expensive. For this reason, windshield wiper drive devices of this type have until now been used primarily in motor vehicles in the upper price class, even though they have advantages that would make it desirable to use them more broadly. Specifically, while in drive devices with an eccentric mechanism the range of motion of the windshield wiper is predetermined by the eccentric mechanism, and accordingly a redesign of the drive device is needed for every vehicle model with a different range of motion, in a drive device with a reversing motor, it suffices to change the positions of a detector or a detectand, in order to thereby adapt the range of motion of the windshield wiper to the given conditions of each individual vehicle model. This flexibility of windshield wiper drive devices with a reversing motor moreover makes them especially well suited for use in windshield wiper systems with a recessed parking position.
The windshield wiper drive device is distinguished by its simple and flexible layout, which enables economical manufacture of the drive device and thus its use even in less-expensive vehicle models, and which also makes it simpler to adapt the windshield wiper drive device to the given conditions of arbitrary models of vehicles. According to the invention, it in fact suffices to detect merely a single given point of the range of motion of the windshield wiper directly with a detector; from this point, the sideways motion of the windshield wiper can be measured relatively with the aid of an incremental transducer, which in principle makes it possible to detect an arbitrary number of positions of the windshield wiper using a detector. The location of the turning points of the windshield wiper is defined by their distance from the point of the range of motion detected by the detector. How great this distance should be in one or the other direction of motion of the windshield wiper can be specified to the control circuit to suit, depending on the circumstances in which the windshield wiper drive device is used.
Especially if only two positions of the windshield wiper, namely the turning point positions, have to be detected, then the simplest option is for the defined distance from the given position to the turning point position to be the same for both directions of motion.
In an especially preferred further refinement of the invention, the control circuit includes a delay element, in order to reverse the direction of motion of the motor also whenever a certain time has elapsed since the passage of the windshield wiper through the given position. Specifically, if the motion of the windshield wiper is blocked by some obstacle, such as snow that has slid off the windshield, or the like, and for this reason the windshield wiper can no longer reach its turning point position, then in this further refinement the control circuit can reverse the direction of motion of the motor even before the actual turning point position is reached and can thus maintain wiper operation over a more limited range of motion. The delay element can be operative either for both directions of motion of the windshield wiper or selectively for only one of the two directions.
In a further preferred embodiment, it is provided that the detector, between a first of the two turning point positions of the windshield wiper and the given position, detects a signal having a first value that originates at a detectand, and detects a second value between the given position and the second turning point position. As a result, it is possible for the control circuit, when the windshield wiper drive device is turned on, to decide by calling up the signal value detected by the detector which side of the given position the windshield wiper is located on, and to select its initial direction of motion accordingly. The direction of motion is expediently selected such that the windshield wiper moves toward the given position, so that upon the passage through the position, the detector detects a change in the signal, on the basis of which the measurement of the relative travel distance measurement can be initialized with the aid of the incremental transducer.
Preferably, the detector and the detectand execute a motion relative to one another that is coupled to the motion of the windshield wiper. To that end, the detectand will mainly be secured to a mechanism that follows the reciprocating motion of the windshield wiper, while conversely the detector is stationary.
Various different designs of the detector and detectand are possible. For instance, the detector can be a magnetic field sensor, such as a Hall sensor, and the detectand can be a magnet pole whose field interacts with the magnetic field sensor. Alternatively, a wiper contact as the detector and a conductive surface connected to a given potential as the detectand, or a photodetector as the detector and a window in an opaque surface or an opaque region on a transparent substrate as the detectand can be considered.
To realize a windshield wiper parking function in the windshield wiper drive device of the invention, the control circuit is preferably equipped with a turn-off function; when the turn-off function is activated, the control circuit does not reverse the direction of motion of the motor when the windshield wiper has reached the first turning point position, but instead turns off the motor when the windshield wiper has reached an extreme position located on the far side of this turning point position.
This extreme position can, just like the turning points, be ascertained by using the incremental transducer to track the distance traversed by the windshield wiper from the given point.
Alternatively, it is possible to design the detectand in such a way that the signal detected by the detector at the extreme position changes over from the first to the second value. In that case, the reaching of the extreme position can also be determined directly with the aid of the detector.
In a further refinement, it is provided that an auxiliary detectand adjoins the detectand on the far side of the extreme position. This auxiliary detectand will never be detected by the detector during normal operation of the windshield wiper drive device; but if it is detected, this is an indication that an error has occurred in the coupling of the relative motion of the detector and the detectand to the motion of the windshield wiper, for instance because the windshield wiper has not been secured to its shaft in the correct position, so that the error has to be corrected to enable error-free operation of the windshield wiper.
Depending on the operative principle of the detector, the auxiliary detectand may for instance be a succession of alternating magnet poles, which in their motion in the detection range of the detector lead to a rapidly alternating signal, or a conductive surface connected to a second potential, or a partly transparent surface.